The present invention relates to a method for controlling electromagnetic actuators for operating induction and exhaust valves of internal combustion engines.
As is known, there are currently under development propulsion units in which the operation of the induction and exhaust valves is managed by means of the use of electromagnetic actuators which replace the purely mechanical distribution systems (camshafts). Whilst, in fact, conventional distribution systems require the definition of a valve lifting profile which represents an acceptable compromise for all the possible operating conditions of the engine, the use of an electromagneticaly controlled distribution system makes it possible to vary the phase as a function of the operating point of the engine in such a way as to obtain an optimal efficiency in all operating conditions.
Therefore various control methods have been developed which allow the valves to be operated by means of the electromagnetic actuators in dependence on the desired timing and position and velocity profiles. Moreover they must avoid the possibility that, during time intervals when the valve is stationary, in which the valves are maintained shut in the closure position or in the fully open position, possible disturbing forces may cause unwanted displacements of the valves themselves. In fact, even partial unwanted opening or closing, if not rapidly opposed, can significantly alter the design flow of air from the induction manifold towards the cylinders, thereby degrading the performance and efficiency of the engine.
The known methods, moreover, have several disadvantages. According to these methods, in fact, for the purpose of opposing the disturbing forces which act on the valves and retaining or rapidly returning the valves themselves into the respective desired positions, during the time periods when the valves are stationary the electromagnets must be supplied with electrical currents which are significantly greater than the minimum currents required in nominal conditions. Moreover, the overall duration of the time period for which each valve is stationary is in one engine cycle, significantly greater than the time period for which it is in motion. There is, therefore, a high consumption of electrical energy caused by the fact that, for almost the entire duration of each engine cycle the current consumed by the electromagnets must be sufficient not only to maintain the valves in the desired nominal conditions, but also to guarantee a margin of safety with respect to possible unwanted displacements. This high consumption detrimentally affects the overall efficiency of the engine, reducing it disadvantageously.
The object of the present invention is to provide a method for the control of electromagnetic actuators which will be free from the described disadvantages and, in particular, which will allow the overall consumption of electrical energy to be reduced.
According to the present invention there is provided a method for controlling electromagnetic actuators for operating induction and exhaust valves in internal combustion engines, where an actuator connected to a control unit is coupled to a respective valve having a real position and comprising a magnetically actuated element, moveable by means of a resultant force to control the movement of the said valve between a closure position and a fully open position; the said control unit being connected to piloting means and comprising supervision means, open loop control means, closed loop control means and selector means controlled by a switching signal generated by the said supervision means; the said first selector means being operable to connect the said piloting means selectively to the said open loop control means and the said closed loop control means; the method being characterised by the fact that it comprises the steps of:
a) operating in an open loop real position control mode;
b) operating in a closed loop real position control mode; and
c) alternatively selecting the said open loop control mode and the said closed loop control mode.